FISH HEALTH MANAGEMENT 333 



the intermediate host snails. In most cases, however, blood flukes are debil- 

 itating but not the cause of serious losses of fish. It is conceivable that 

 large numbers of miracidia leaving the gill at one time could cause a signif- 

 icant loss of blood and damage to the gills. Eggs and developing miracidia 

 also interfere with the circulation of blood in the gill capillaries and in the 

 capillary beds of the kidney and liver. 



Copepod Parasites 



Most copepods in fresh and salt water are an important part of the normal 

 diet of fish. Certain species, however, are parasitic on fish and the sites of 

 their attachment may become ulcerated and provide access for secondary 

 infections by fungi and bacteria. Crowded hatchery rearing units provide 

 ideal conditions for infestations by copepods because of the dense fish pop- 

 ulations and rich environmental conditions. Under most hatchery condi- 

 tions, however, serious losses of fish seldom are caused by parasitic 

 copepods. The stocking of copepod-infested fish has infected wild fish in 

 streams. 



Figure 103. Sanguinkola davisi, 2,000x magnification. (Courtesy G. L. Hoff- 

 man, Fish Farming Experimental Station, Stuttgart, Arkansas.) 



